Sewer pipes and buried conduits often become cracked or broken after long periods of time spent underground. Previously, in order to repair such cracks and breaks, the pipes and conduits would have to be replaced. Replacement involved excavating the pipe or conduit from the ground and burying a new section. This process was expensive and time consuming, and also required the pipe or conduit to be out of service for long periods of time. Methods for repairing cracks and breaks in conduits and pipes were developed whereby the conduits or pipes need not be excavated in order to be repaired. These methods included the use of inserts to act as new conduit and pipe walls.
Methods for repairing conduits using inserts are well known. Known inserts use mechanical as well as chemical means for creating and bonding the insert to the repaired pipe. Methods and apparatus have also been disclosed that use resin impregnated fibrous material to repair cracks and fissures in conduits and low pressure pipes, such as that disclosed in U.S. Pat. No. 5,049,003. These methods call for a single layer matting material to be impregnated with uncured resin, drawn into the conduit, expanded with an inflation device and left to cure. Because the curing process is extended (as much as 24 hours) and the site must be attended during the entire process, some methods call for heat to be applied to the resin impregnated matting by means of hot water or hot air pumped continually through the inflation device. There are significant drawbacks to these methods. First, the single layer matting material must be coated on the inside with a releasing agent to permit release of the inflation device once the resin has cured. Second, the resin impregnated matting material must bond to the surface of the conduit to ensure adequate sealing against leakage. If fluid is leaking into or out of the conduit being repaired, the resin material may wash out of the matting material before it cures or be diluted and neither adequate strength of the liner nor an adequate bond between the insert liner and the conduit may be maintained. Also, during the insertion process, material may accumulate on the outside of the resign impregnated insert matting material, thereby reducing available bonding surface and consequently strength and sealing capabilities of the repair. Also, during the insertion process, void areas where resin is not present can occur in the matting material, thereby causing areas of weakness and areas where the liner fails to properly bond to the conduit.
Finally, some systems call for heating the insert to decrease resin curing time. Unfortunately providing heated water or air for an extended period of time requires a great amount of energy as well as additional equipment in the form of heating devices thereby increasing costs and capital expenditure.
Methods and apparatus calling for multiple layer liner inserts are also well known. These methods generally add a protective coating to the outside of the resin impregnated matting material to protect against accumulation of material during insertion of the insert into the conduit and to prevent wash out during the curing process. Some methods use the outer lining only during transport of the liner into the conduit to be repaired. These methods call for the liner system to be inverted, installed and inverted again to place the resin impregnated material in contact with the inner conduit wall. Problems with these methods include requiring special devices to invert the liner once it has been placed inside the conduit and limitations on ease of use. Other methods and apparatus also call for an inner layer to be added to a liner system to form a three layer insert wherein the inner layer is used to accomplish release and removal of the inflation device, without mandating use of a releasing agent on the insert matting material.
Still other methods are also known wherein electrical wiring and voltage applied thereto is used to generate heat within an insert, such as disclosed in U.S. Pat. No. 4,768,562. In this method a prefabricated hardened resin impregnated liner is heated to allow outward pressure from an inner rubber tube to force a resin impregnated matting material in contact with the inner wall of the conduit to be repaired. The limitation in the prior art regarding material accumulation during insertion, resin voids during curing and wash out are also present in this method. Further, the inflation means (rubber tube) used in this method remains inside the insert, further constricting the conduit, and the electrical wiring used for the heating process is placed within the resin impregnated matting material, adding costs to the matting material. This method does not utilize the heat for quicker curing, but instead, heats the resin to allow pressure from the inner elastomeric tube to expand the resin impregnated material liner to the correct overall interior size of the conduit.